Removal of sulfur compounds from gas streams has been of considerable importance in the past and is even more so today due to environmental considerations. Gas effluent from the combustion of organic materials, such as coal, almost always contains sulfur compounds and sulfur removal processes have concentrated on removing hydrogen sulfide since it has been determined to be a significant health hazard. With increasing emphasis on the elimination of sulfur discharge to the atmosphere and the utilization of natural gas streams that were heretofore unusable due to their sulfur content, attention is turning to the removal of sulfur compounds from gas streams.
The process of the present invention provides a finishing means for the removal of low level concentrations of mercaptans, sulfides and disulfides from a gas stream, specifically natural gas.
Numerous natural gas wells produce what is called in the industry "sour gas." Sour gas is natural gas that contains hydrogen sulfide, mercaptans, sulfides and disulfides in concentrations that make its use unacceptable. Considerable effort has been expended to find an effective and cost efficient means to remove these objectionable sulfur compounds from natural gas. The commercially available processes for the desulfurization of natural gas have been primarily concerned with the removal of hydrogen sulfide. At present the interstate pipeline system for natural gas has a limit of one-quarter gram or 4 ppm of hydrogen sulfide. This can usually be obtained by the use of alkanol amine, iron sponge and zinc compound processes. However, none of these processes are suitable or effective for treatment of natural gas containing low levels of mercaptans, sulfides and disulfides.
U.S. Pat. No. 4,283,373 by the present inventors discloses a process which consists of contacting a gas stream with alkali metal salts of sulfonamides or resins containing sulfinamide functionalities in the presence of an iron sponge bed. Further, U.S. Pat. No. 4,311,680 discloses a process wherein an iron sponge bed is enhanced through the use of hydrogen peroxide. These processes and others contained in U.S. Pat. Nos. 632,400, 1,934,242, 4,027,002, 4,238,463 and 4,278,646 all describe processes resulting in the removal of most of the hydrogen sulfide. Some work has demonstrated that some of the mercaptans, as well as some of the sulfides and disulfides and residual sulfides are removed. However, these processes do not meet the more severe demands placed on special uses of natural gas or gas streams where lower sulfur levels are required.
A very pure natural gas is required for foundry applications wherein metals susceptible to sulfur poisoning or degradation are melted or alloyed. Specifically, furnaces which melt aluminum alloys require extremely low sulfur gas since the sulfur compounds react with aluminum. Aluminum alloys can be directly fired by natural gas in graphite crucibles; however, the graphite crucible is porous to gases so that the molten aluminum alloy absorbs sulfur compounds which are converted to aluminum sulfide. The presence of this sulfide adversely affects the alloy so that poor molds are obtained. Thus, it has been found desirable to reduce total sulfur to 1 to 6 ppm level in the natural gas.
There is a present need for an efficient low cost finishing process which will essentially remove all of the mercaptans, sulfides and disulfides from a gas stream.
All the references cited do not suggest or disclose a process for the removal of mercaptans, sulfides, disulfides and residual sulfides from a gas stream through the use of a scrubbing solution which consists of hydrogen peroxide alone or in combination with ammonia or an amine.